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Evaluating the pelletization of “pure” and blended lignocellulosic biomass feedstocks

Crawford, Nathan C., Ray, Allison E., Yancey, Neal A., Nagle, Nick
Fuel processing technology 2015 v.140 pp. 46-56
Miscanthus, Panicum virgatum, biofuels, biomass, cohesion, compressibility, corn stover, economic sustainability, energy, feedstocks, friction, lignocellulose, models, pelleting
Due to its low density and poor flowability, raw biomass may not be an economically viable feedstock for the production of biofuels. However, mechanical densification can be employed to improve its viability. In this study, the flow properties (compressibility, shear, and wall friction) of “pure” feedstocks (corn stover, hybrid poplar, switchgrass and Miscanthus), and feedstock blends, are investigated and compared to measured pelleting energy consumption values. As anticipated, the more compressible materials required lower pelletization energies. Conversely, the less flowable feedstocks (i.e., the materials with higher cohesion and yield strength) were less energy intensive to pellet. In addition, the flowability parameters of the blended materials could be predicted by averaging the measured flow parameters of their pure feedstock constituents. Therefore, only the flow characteristics of the pure feedstocks need to be directly measured, while the flowability of a blended feedstock with a known blend ratio can be accurately inferred. A model was also developed to calculate the required pressure to pellet a particular feedstock, pure or blended, based on its flowability parameters (namely compressibility and wall friction). Strong correlation was observed between the measured pelleting energy consumption and the predicted pelleting pressure values. This newly developed model allows for a material's pelleting feasibility to be assessed without having to physically pelletize the material.